The present invention relates to microwave oscillators and more specially to FET stable microwave oscillators.
Stable microwave oscillators have recently been developed by using a field-effect transistor and a temperature stable dielectric-ceramic resonator. Such an oscillator is disclosed, for instance, in MTT-26, volume 3, March 1978, IETT Transaction on Microwave Theory and Techniques, and uses a field-effect transistor and a BaTi.sub.4 O.sub.9 resonator. Known oscillators of this type only use a single resonator and should include stabilization or matching circuits, in the form of active or passive systems obtained according to microstrip technique on an alumina substrate.
Similarly to former oscillators, this type of oscillator only includes a single output and is subject to some limitations, such as for instance a low quality rating, owing to the poor overvoltage of microstrip line resonators, the loss of energy resulting from the stabilization system, and the severe hazards of stray frequencies.
The present invention relates to a microwave oscillator having a simple, solid state construction, eliminating the energy losses resulting from a stabilization system, allowing reduction in the hazards of stray frequencies and showing a very high quality rating with, as a consequence, a very low noise level and a substantial reduction of the load effect.
Another aspect of the present invention is the provision of an oscillator of the above-mentioned type having at least two outputs which can be used simultaneously and therefore allow, in the embodiments where it is included, to reduce the number of passive microwave devices such as power coupling or dividing devices.
To this end, according to a feature of the present invention, the transistor microwave oscillator includes a first resonating circuit having a dielectric resonator connected to a first terminal of said transistor and a second resonating circuit having a dielectric resonator connected to a second terminal of said transistor, and means for biasing said transistor, the dielectric resonators of said first and second resonating circuits being similar and operating at the same resonating frequency.
According to a second feature of the invention, the solid state oscillator construction includes resonating circuits made by applying the microstrip technique to an insulating substrate, the ceramic-dielectric resonators being coupled to microstrips in the TE.sub.01.delta. mode, said transistor being a bipolar transistor, or, advantageously, a field-effect transistor.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.